In industrial power transmission arrangements, the keyway is the almost universally accepted medium to secure gears, sprockets, bosses, bearings and other power transmission devices to a shaft, so as to rotate therewith, without relative rotation between the shaft and the transmission member. However, a key is a stress riser by its engaging only one location at the circumference of a shaft and by its sharp, abrupt edges. In some uses, such as for example, with gears, keyways make the gears difficult to balance. In the middle of a shaft, milling a keyway is awkward and time-consuming machine work.
Other well known methods of securing a power transmission device to a shaft include the use of splines and polygon connections.
Splines are very satisfactory, but generally too expensive for small industrial production quantities of some products. Polygon connections include special shaft and bore shapes which must be precision formed. These connections are suitable for heavy shock load, but because the shafts have to be precision formed and ground -- an expensive manufacturing operation -- their use is generally limited to special purposes.
Another form of connection for adapting a power transmission member to a shaft is the tapered bushing. In this connection, the bore of the transmission member must be tapered to match the bore of the bushing. Machine bolts or cap screws are used to draw the tapered bushing into seating engagement with the bore of the transmission product. The screws must be tightened alternatively and progressively until the bushing is pulled up tight -- a time consuming operation, which is manually performed.